The following formula (I) can be attributed to the alpha-arylpropionic acids obtainable according to the present invention: ##STR1## wherein Ar represents either an aromatic, or a heteroaromatic group containing one or more rings, however linked together, having globally up to 20 carbon atoms, such as phenyl-, naphthyl-, diphenyl- and thienyl groups. Said Ar group may in its turn also be substituted by groups inert under reaction conditions. Compatible groups are e.g.: alkyl-, cycloalkyl- and aryl-groups, also optionally substituted, halogens, alkoxyl groups, phenoxyl groups, ketonic groups.
Only recently research has turned towards carbonylation of substrates of the secondary benzyl type, such as for instance secondary aryl-alkyl halids, which carbonylation, besides considerations on the reaction mechanism involved, meets also operational difficulties with regard to the possible yields, etc.
Prior Art literature on the matter is not particularly exhaustive, especially with regard to the aspect of the commercial production.
It can, however, practically be stated that, up to this date, the alpha-aryl-propionic acids and the alkaline salts thereof, object of the present invention, were prepared by hydrolysis of the corresponding nitriles; or by reaction of CO.sub.2 with Grignard compounds; or by,the decarbonylation of malonic derivatives or else by oxidation of structurally suitable alcohols or aldehydes, or finally by reduction of aryl-acrylic acids etc.
It is a question of methods technologically removed from the process object of the present invention, which methods are characterized by the fact of being polystages, non-catalytic and essentially complicated by the use of reactants difficult to be found and/or handled, with the resulting corresponding operational and economical burdens which make such methods of little practical commercial attractiveness.
On the other hand, there have recently been suggested catalytic methods for the preparation of alpha-aryl-propionic acids.
According to one of these methods, substituted alpha-aryl-propionic acids or alkyl esters thereof are prepared by means of either hydrocarboxylation or hydrocarbalkoxylation of substituted aryl-ethylenes in an aqueous or alcoholic medium, catalyzed by Palladium complexes, preferably in the presence of acids.
Nevertheless, the commercial interest offered by the above mentioned method does not seem high. As a matter of fact, the method foresees, amongst others, the use of expensive Pd complexes as catalysts and of very high CO pressures.
There have also been reported possibilities for carbonylation reactions of halogen derivatives of the secondary benzyl type with Pd and Co complexes.
In the first instance, there has been foreseen the use of expensive catalysts such as arsinic Pd complexes, under CO pressure. Moreover, the esters are obtained with rather poor yields and selectivities.
In the second instance, the method foresees the formation of esters using alkaline alcoholates in the presence of dicobalt-octacarbonyl. In this latter case, too, the yields and selectivities that are obtainable by the method are rather poor. In fact, there are substantially obtained quantities of ethers and esters of the linear acid. This involves however operational burdens in the separation and purification of the products.
Moreover, a further economical burden is represented by the use of alcoholates under strictly controlled pH conditions.
Finally, the reaction proves to be limited to the phenyl derivatives only, possibly only alkyl-substituted derivatives.